Digital controlled document feeder

ABSTRACT

A document sheet feeder for use with a recycling electrostatic copier having a moving photoreceptor, provides means to insure the imaging of the document on the photoreceptor in registration with a desired pitch frame of the photoreceptor, by comparing and correcting the position of the leading edge of each document sheet relative to the appropriate pitch line of the photoreceptor. A pulse generator is keyed to the movement of the photoreceptor and provides a pulse train output that is a digital reference of the position of the photoreceptor. As a document sheet passes a reference point in its feed path, its leading edge is detected and compared to the position of the photoreceptor. The document sheet is then accelerated or retarded relative to normal feed velocity by an amount which properly relates the document to the appropriate pitch frame of the photoreceptor.

United States Patent [1 1 Rodek et al.

[ 1 DIGITAL CONTROLLED DOCUMENT FEEDER [75] inventors: Victor Rodek,Rochester; Raymond G. Ticknor, Fairport, both of NY.

[73] Assignee: Xerox Corporation, Stamford.

Conn.

[22] Filed: Jan. 31, 1974 [21] Appl. No.: 438,489

[52] U.S. Cl 355/14; 355/8; 355/3 R [51] Int. Cl. G03g 15/04; (303g15/00 [58] Field of Search 355/3 R, 8, 14; 271/9, 271/265, 266, 270,202, 203

[5 6] References Cited UNITED STATES PATENTS 3,719,267 3/1973 Reist etal 198/76 Primary ExaminerRobert P. Greiner Attorney, Agent, orFirm.lames J. Ralabate; William A. Henry, I]

[ June 10, 1975 [57] ABSTRACT A document sheet feeder for use with arecycling electrostatic copier having a moving photoreceptor, providesmeans to insure the imaging of the document on the photoreceptor inregistration with a desired pitch frame of the photoreceptor, bycomparing and correcting the position of the leading edge of eachdocument sheet relative to the appropriate pitch line of thephotoreceptor. A pulse generator is keyed to the movement of thephotoreceptor and provides a pulse train output that is a digitalreference of the position of the photoreceptor. As a document sheetpasses a reference point in its feed path, its leading edge is detectedand compared to the position of the photoreceptor. The document sheet isthen accelerated or re tarded relative to normal feed velocity by anamount which properly relates the document to the appropriate pitchframe of the photoreceptor.

5 Claims, 2 Drawing Figures DIGITAL CONTROLLED DOCUMENT FEEDER SUMMARYAND BACKGROUND OFINVENTION The present invention relates to sheetfeeders, and more particularly to the registration of documents along afeed path therefor relative to the operational cycle of a documentprocessing machine, such as an electrostatic document copying machine.

In one form of electrostatic copying machine. for example, a documentsheet to be copied is moved past a scanning slit, and an image of thedocument is focused on a photoreceptor drum or endless belt that isrotated at an angular velocity which provides a linear speed for thephotoreceptor surface that is equal to the linear speed of the document.The electrostatic image thus formed on the photoreceptor may bedeveloped with electroscopic toner powder, and the toner imagetransferred to a receiving sheet. The photoreceptor surface is thencleaned of any residual toner, the residual electrostatic image isdischarged from the photoreceptor, and the photoreceptor is prepared tobe recycled for copying another document sheet fed past the scanningslit. The photoreceptor may be sufficiently large to hold severaldocument sheet images simultaneously on its surface. In automaticcopying machines, a plurality of document sheets may be fedautomatically for successive imaging on the photoreceptor, and forcertain purposes it is important that the image of each sheet appear ata particular pitch frame or angular location on the photoreceptor.

In accordance with the present invention, document sheets to be copiedare fed one by one from a document holding station or magazine to apitch frame registration station, and thence to the document scanningand imaging station where an image of the document sheet is focused onthe moving photoreceptor drum or belt. The speed of travel of thedocument sheet at the scanning station is predetermined and mustcorrespond to the photoreceptor speed for proper imaging of the documentsheet. However, before the document sheet reaches the scanning andimaging station, its speed of travel may be varied, and this is done atthe pitch frame registration station to locate the leading edge of thedocument sheet at a proper reference point in its path of travelrelative to the position of the photoreceptor. When this isaccomplished, the document sheet leading edge will reach the documentscan station in coincidence with the arrival of the pitch line of thepitch frame in which the document sheet is to be imaged.

To accomplish this registration of the document in its path of travel,the present invention utilizes an electrical pulse generator that iskeyed to the movement of the photoreceptor, to establish a digitalreference of the position of the photoreceptor. The passage of thedocument sheet leading edge over a reference point in its path of travelis sensed to produce an electrical sig nal. The time of occurrence ofthis document signal is compared with the pulse train indication of theposition of the photoreceptor. If said document signal coincides withthe appropriate pulse of said pulse train, the document is in properposition relative to that of the photoreceptor to arrive at the scanstation in coincidence with the desired pitch frame of thephotoreceptor, utilizing the established rate of advance for thedocument feed conveyor. However, if the document signal lags or precedesthe appropriate pulse of the pulse train, the document sheet isaccelerated or retarded an increment corresponding to the number ofpulses in the pulse train by which the document signal is out ofsynchronism with the appropriate pulse of the pulse train. This actionplaces the document sheet at the appropriate point in its feed path tobring it to the scan station in coincidence with the appropriate pitchframe of the photoreceptor.

It is therefore one object of the present invention to provide for theregistration of a sheet along a feed path therefor relative to theoperational cycle of a machine to which the sheet is being fed.

Another object of the present invention is to provide for theregistration ofa sheet along a feed path therefor relative to areference indication.

Another object of the present invention is to provide for theregistration ofa sheet along a feed path therefor relative to areference indication, by accelerating or retarding said sheet in itspath of travel by an increment corresponding to the discrepancy betweensheet location and said reference indication.

Still another object of the present invention is to provide for theforegoing registration of a sheet along a feed path therefor, whereinsaid sheet is a document sheet being fed to a document copier.

Other objects and advantages of the present invention will becomeapparent to those skilled in the art from a consideration of thefollowing detailed description of one exemplary embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS The following description of theinvention is had in conjunction with the accompanying drawings, in whichlike reference characters refer to the same or corresponding parts, andwherein:

FIG. 1 is a schematic illustration of a sheet feeder for deliveringsuccessive document sheets to an electro static document copier; and

FIG. 2 is a schematic illustration of an apparatus for controlling thesheet feeder of FIG. I to accomplish registration of the document sheetsalong their feed path relative to the operational cycle of the documentcopier.

DETAILED DESCRIPTION The document sheet feeder and copier illustrated inFIG. 1 comprises a magazine 11 for holding a stack of document sheets12. A pressure pad 13 bears on top of the stack I2 enabling the belt 14to feed sheets one by one from the bottom of the stack toward a sheetseparator 15. If more than one sheet is fed to the separator 15, theupper sheet or sheets are held from further advance by the upper retardroll 16, while the bottom sheet is fed by the bottom roll l7 to the nipof drive rolls l8, and thence to the feed belt 19 which delivers eachdocument sheet to and past the scanning sperture 20 of the electrostaticcopier 50. Each sheet leaving feed belt I9 is conveyed by guide chute 21to the pair of endless conveyor belts 22 and 23 which return the sheetsto the top of the stack 12 in magazine 11 in readiness for recycling, ifdesired. Endless belts 22 and 23 are driven in synchronism by drums 24and 25, whose shafts are keyed together by drive chain 26.

A tacking corona discharge device 27 is utilized at the input side offeed belt 19, to cause each sheet to adhere to the belt 19 byelectrostatic attraction, and a detacking corona discharge device 28 isprovided at the output side of belt 19 to facilitate the removalofsheets from the belt and their delivery to the chute 21.

The scanning slit 20 focuses the moving image of a document sheetcarried by belt 19 onto the surface of photoreceptor drum 51 ofconventional electrostatic copier 50. Drum 51 is rotated by shaft 52past the scanning slit 20 in synchronism with the movement of a documentsheet on belt 19 past said slit. Thus, the speed of belt 19 and theperipheral speed of drum 51 are made equal, and it is likewise desirablethat feed rolls l8 deliver each document sheet to belt 19 at the samespeed of travel.

The electrostatic copier 50 is shown as having a plurality of imageprocessing stations positioned about its periphery. An electrostaticcharging station 53 is located just in advance of the image exposurestation formed by scanning slit 20, and an image developing station 54is located immediately following the scanning slit. The developingstation is followed by an image transfer station 55, which is followedby a residual image cleaning station 56, and an electrostatic imageerasing station 57.

The document sheet feeding apparatus 10 and the electrostatic copierapparatus 50 as thus far described are composed of well knowncomponents, and the structure and operation of the components and of thesystem as a while will be readily understood by those skilled in theart.

The rate of peripheral speed of photoreceptor drum 5] and linear speedof feed belt 19 must be the same in order to obtain a clear image ofthedocument sheets on the drum 51. Likewise the rate of feed of thedocument sheets by feed rolls 18 should preferably be the same as thatobtained by feed belt 19. However, the speed at which a document sheetis fed by sheet separator toward the feed rolls 18 can be varied, andthis feature is used to bring each document sheet into registrationwhich the appropriate pitch frame therefor on photoreceptor drum 5]. Forthis purpose, a photodetector indicated at 31 is positioned betweensheet sepa rator l5 and feed rolls l8, and is used as the referencepoint in locating the leading edge of each sheet as it is fed toward thecopying station.

The registration control system is schematically shown in FIG. 2. Theangular position of photoreceptor drum 51 is constantly monitored byutilizing its drive shaft 52 to drive a pulse generator 32. Thegenerator 32 may, for example, generate 360 pulses per revolution ofshaft 52, and its pulse train output would therefore represent theangular position of the drum 51 to the nearest degree. The output ofgenerator 32 is fed to a power amplifier, counter and discriminatorcircuit generally designated by the numeral 33. A second input tocircuit 33 is obtained from the photodetector 31, which is used toidentify the passage ofthe leading edge of each document sheet at theregistration point in the sheet feed path.

Circuit 33 compares the time of occurrence of the leading edge of adocument sheet at the registration point with the angular position ofthe photoreceptor drum 51. If the relationship is proper to relate thedocument sheet to its appropriate pitch frame on the drum 5]. there isno registration correction output from the circuit 33, and the documentfeed continues in the manner above-described. However, if therelationship is not proper. the amount of correction is measured incircuit 33, and it operates a control drive to either accelerate ordecelerate the document sheet by an appro priate amount, depending uponwhether the sheet is lagging or leading its appropriate pitch framelocation.

The registration control system operates on and is the drive for sheetseparator roll 17. A first stepping motor 34 is driven by the circuit 33in accordance with the pulse output of generator 32. The motor 34 thusdrives separator feed roll 17 through differential 35 and a gear andbelt drive train at a rate directly controlled by rotation of drum 51.

The differential 35 has a second drive input from stepping motor 36.Stepping motor 36 is driven an appropriate amount forward or backward asdetermined at circuit 33 by comparing the input from photodetector 3]with the angular position of the drum 5]. This action either speeds upor slows down the drive of roll 17, and hence accelerates or deceleratesthe feed of the document sheet by that amount required to place it inproper relation to its appropriate pitch frame on the photoreceptor drum5].

It will thus be appreciated, as each sheet passes from sheet separator15 toward feed rolls 18, its leading edge is detected by photodetector3]. The occurrence of this signal is compared with the angular positionof drum 5] by circuit 33, and its relation to an appropriate pitch frameon the drum is determined. Roll 17 of sheet sepa rator 15 is operatedthrough differential drive 35, and by means ofa normal power input fromstepping motor 34 and a correctional power input from stepping motor 36,roll 17 advances the document sheet at a rate that places it inregistration with its appropriate pitch frame on photoreceptor drum 51.

While a drum type xerographic reproduction machine employing scanexposure has been illustrated and described, it should be understoodthat the invention may also be practiced with a reproduction machineemploying a photoreceptor in the form of a belt utilizing a scanexposure, or, if the surface of the belt opposite the document ismaintained in a planar condition, flash exposure might also be utilizedwithout departing from the scope of the present invention.

What is claimed is:

1. Sheet feeding and processing apparatus comprising, first sheetconveyor means, second sheet conveyor means, cyclic processing meansincluding an electrostatic photocopier having an endless andrepetitively cycling photoreceptor cooperating with a sheet on saidsecond conveyor means, means for identifying the cyclic position of saidphotoreceptor. means between said first and second conveyor means fordetecting the presence of a sheet. means for relating the detection of asheet by said detection means to the cyclic position of saidphotoreceptor as determined by said identifying means. and meansresponsive to said relating means for momentarily varying the speed ofsaid first conveyor means to correct any deviation from a predeterminedrelationship between said cyclic position of said processing means andsaid detection of the presence of a sheet.

2. Sheet feeding and processing apparatus as set forth in claim 1,wherein said identifying means comprises a pulse generator meansoperated by said processing means.

3. Sheet feeding and processing apparatus as set forth in claim 2,wherein said first conveyor means includes a first drive meanscontrolled by said pulse generator means.

4. Sheet feeding and processing apparatus as set forth 5. Sheet feedingand processing apparatus as set forth in claim 3, wherein said meansresponsive to said rclatin claim 4, and including a differential forcombining ing means comprises a second drive means coupled to said firstand second drive means. said first conveyor means.

1. Sheet feeding and processing apparatus comprising, first sheetconveyor means, second sheet conveyor means, cyclic processing meansincluding an electrostatic photocopier having an endless andrepetitively cycling photoreceptor cooperating with a sheet on saidsecond conveyor means, means for identifying the cyclic position of saidphotoreceptor, means between said first and second conveyor means fordetecting the presence of a sheet, means for relating the detection of asheet by said detection means to the cyclic position of saidphotoreceptor as determined by said identifying means, and meansresponsive to said relating means for momentarily varying the speed ofsaid first conveyor means to correct any deviation from a predeterminedrelationship between said cyclic position of said processing means andsaid detection of the presence of a sheet.
 2. Sheet feeding andprocessing apparatus as set forth in claim 1, wherein said identifyingmeans comprises a pulse generator means operated by said processingmeans.
 3. Sheet feeding and processing apparatus as set forth in claim2, wherein said first conveyor means includes a first drive meanscontrolled by said pulse generator means.
 4. Sheet feeding andprocessing apparatus as set forth in claim 3, wherein said meansresponsive to said relating means comprises a second drive means coupledto said first conveyor means.
 5. Sheet feeding and processing apparatusas set forth in claim 4, and including a differential for combining saidfirst and second drive means.